abstract

Can one declare a static method within an abstract class, in Dart?

由 安稳与你 提交于 2020-04-12 20:59:07
问题 In an abstract class , I wish to define static methods, but I'm having problems. In this simple example abstract class Main { static String get name; bool use( Element el ); } class Sub extends Main { static String get name => 'testme'; bool use( Element el ) => (el is Element); } I receive the error: function body expected for method 'get:name' static String get name; Is there a typo in the declaration, or are static methods incompatible with abstract classes? 回答1: Dart doesn't inherit

Can one declare a static method within an abstract class, in Dart?

由 故事扮演 提交于 2020-04-12 20:52:25
问题 In an abstract class , I wish to define static methods, but I'm having problems. In this simple example abstract class Main { static String get name; bool use( Element el ); } class Sub extends Main { static String get name => 'testme'; bool use( Element el ) => (el is Element); } I receive the error: function body expected for method 'get:name' static String get name; Is there a typo in the declaration, or are static methods incompatible with abstract classes? 回答1: Dart doesn't inherit

Can one declare a static method within an abstract class, in Dart?

由 允我心安 提交于 2020-04-12 20:51:09
问题 In an abstract class , I wish to define static methods, but I'm having problems. In this simple example abstract class Main { static String get name; bool use( Element el ); } class Sub extends Main { static String get name => 'testme'; bool use( Element el ) => (el is Element); } I receive the error: function body expected for method 'get:name' static String get name; Is there a typo in the declaration, or are static methods incompatible with abstract classes? 回答1: Dart doesn't inherit

abstract class和interface的使用场景分别是什么？

由 余生颓废 提交于 2020-03-04 10:15:16
abstract class 和 interface 是 Java 语言中对于抽象类定义进行支持的两种机制，正是由于这两种机制的存在，才赋予了 Java 强大的面向对象能力。 abstract class 和 interface 之间在对于抽象类定义的支持方面具有很大的相似性，甚至可以相互替换，因此很多开发者在进行抽象类定义时对于 abstract class 和 interface 的选择显得比较随意。其实，两者之间还是有很大区别的，对于它们的选择甚至反映出对于问题领域本质的理解、对于设计意图的理解是否正确、合理。我认为正确运用好抽象类和接口，可以优化软件结构的设计，对软件的扩展、维护带来很大的便利。本文将对它们之间的区别进行一番剖析，试图给开发者提供一个在二者之间进行选择的依据。 首先来理解一下抽象类。在面向对象的概念中，我们知道所有的对象都是通过类来描绘的，如果一个类中没有包含足够的信息来描绘一个具体的对象，这样的类就是抽象类。抽象类往往用来表征我们在对问题领域进行分析、设计中得出的抽象概念，是对一系列看上去不同，但是本质上相同的具体概念的抽象。比如我们 xpads 项目中的交易类就可以理解为一个抽象类，即期交易、远期交易、掉期交易等都是继承交易类的具体类。即期交易、远期交易、掉期交易这些具体概念是实际存在的，而交易这个概念在问题领域中是不存在的，可以理解为一个抽象概念

Typescript abstract property

由 两盒软妹~` 提交于 2020-02-06 07:56:27
问题 I started learning typescript a few days ago. I know all the major OOP concepts, but I just don't understand the concept behind abstract properties. I understand that you have to override/implement the abstract members of your base class in the child class. But still, what is it used for? I get the concept behind abstract methods, but not this. If you could present me some nice examples, I would really appreciate it. Thank you! 回答1: Abstract properties are useful for similar reasons that

How does the JLS specify the terms “abstract method”, “concrete method” and “default method”?

由 为君一笑 提交于 2020-02-03 05:48:10
问题 I have seen "divergent" definitions of the terms abstract method , concrete method and default method in some StackOverflow answers. What are the real definitions, as given by the Java Language Specification? Please include the relevant supporting JLS references in your answer. 回答1: According to the JLS 8.4.3.1: "An abstract method declaration introduces the method as a member, providing its signature (§8.4.2), result (§8.4.5), and throws clause if any (§8.4.6), but does not provide an

Java static members in a subclass accessed via a generic parent

由 喜夏-厌秋 提交于 2020-01-30 04:22:11
问题 This seems like a newbish question, but the last time I worked with Java, the language didn't have generics. I have a class hierarchy (names changed to be as generalized as possible): public abstract class AbstractBase { .... } public class ConcreateSubA extends AbstractBase { .... } public class ConcreateSubB extends AbstractBase { .... } ... public class ConcreateSubZZ9PluralZAlpha extends AbstractBase { .... } ... I'm trying to clean up some legacy code, and there's one place where a ton

Overriding abstract generic method in Java

由 浪尽此生 提交于 2020-01-23 16:43:28
问题 Problem outline I'm generifying the better part of my current project's base and I had an idea that I decided to test regarding overriding an abstract method. Here are my test classes in Java: public abstract class Base { public abstract <T extends Base> T test(); } First implementation: public class Inheritor extends Base { @Override public Inheritor test() { return null; } } Second implementation: public class Inheritor2 extends Base { @Override public <T extends Base> T test() { return

Why can abstract methods only be declared in abstract classes?

由 …衆ロ難τιáo~ 提交于 2020-01-22 06:55:39
问题 I understand that in abstract classes methods be both abstract, or not. But why can I not create an abstract method in a "normal", non-abstract class? Thanks in advance for any explanation! 回答1: Abstract method basically says, that there is no implementation of the method and it needs to be implemented in a subclass . However if you had an abstract method in a non-abstract class, you could instantiate the class and get an object, that would have an unimplemented method, which you would be

Why can abstract methods only be declared in abstract classes?

由 ぃ、小莉子 提交于 2020-01-22 06:54:27
问题 I understand that in abstract classes methods be both abstract, or not. But why can I not create an abstract method in a "normal", non-abstract class? Thanks in advance for any explanation! 回答1: Abstract method basically says, that there is no implementation of the method and it needs to be implemented in a subclass . However if you had an abstract method in a non-abstract class, you could instantiate the class and get an object, that would have an unimplemented method, which you would be
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